THE RETINA. 



417 



it consists of a pavement of accurately-jointed hexagonal 

 pigmented cells. 



2. The layer of rods and cones, or Jacob's mem- 

 brane, consists of rods and cones, arranged perpendicu- 

 larly to the surface. They each consist of an inner and 

 outer segment, connected together by a cement sub- 

 stance. The outer segments are transversely striated, 

 the inner segments striated and granular. 



3. External limit- 

 ing membrane, a lam- 

 ina of cellular tissue. 



4. Outer nuclear 

 layer, consisting of 

 bipolar cells trans- 

 versely striated, called 

 rod granules. They 

 are connected by one 

 extremity with a rod ; 

 the other enters the 

 outer molecular layer. 

 The cone -granules, 

 less in number, are 

 multipolar, nucleated 

 cells, which are con- 

 nected by numerous 

 processes with the 



cone, and terminate internally in a single pole, which 

 passes into the outer molecular layer. 



5. The outer molecular layer consists of a net-work 

 of delicate fibres, with some ganglion cells. It has a 

 granular appearance. 



6. The inner nuclear layer consists of bipolar, nuclear 

 cells, the poles of which communicate with a ganglion 

 cell and a rod or cone. 



27 



FIG. 179. DIAGRAM OF THE FORMATION 

 OF THK RETINA. 



N, optic nerve ; K. retina ; p, pigment layer : c, choroid. 



